Ms Rudd told MPs it was an "outrageous crime", adding that the government would "act without hesitation as the facts become clearer".

She refused to speculate on whether the Russian state might have been involved in the attack, saying the police investigation should be based on "facts, not rumour".

However, she said the government was committed to bringing the perpetrators to justice "whoever they are and wherever they may be".

Image caption
Detective Sergeant Nick Bailey is now in a stable condition after being treated in intensive care after the incident

Prime Minister Theresa May told ITV News that "if action needs to be taken then the government will do that".

"We will do what is appropriate, we will do what is right, if it is proved to be the case that this is state-sponsored," she said.

Russia has denied it was involved.

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Media captionAmber Rudd said the attack was an "outrageous crime"

Meanwhile, a doctor who was one of the first people at the scene has described how she found Ms Skripal slumped unconscious on a bench, vomiting and fitting. She had also lost control of her bodily functions.

The woman, who asked not to be named, told the BBC she moved Ms Skripal into the recovery position and opened her airway, as others tended to her father.

She said she treated her for almost 30 minutes, saying there was no sign of any chemical agent on Ms Skripal's face or body.

The doctor said she had been worried she would be affected by the nerve agent, but added that she "feels fine".

BBC correspondent Leila Nathoo said there had been "a flurry of activity" outside Mr Skripal's Salisbury home on Thursday.

She said ambulances and an incident response team were in attendance and a police tent had been erected outside the house.

Graves sealed off

Part of a business park in nearby Amesbury also remains cordoned off, while the graves of Mr Skripal's wife and son at a Salisbury cemetery have also been taped off by police.

It comes as police said government scientists have identified the nerve agent used, but will not be making that information public at this stage.

Earlier, Ms Rudd told the BBC the nerve agent used in the poisoning was "very rare".

Defence Secretary Gavin Williamson said Russia was becoming an "ever greater threat", amid speculation the attack could have some element of state involvement.

"Russia's being assertive, Russia's being more aggressive, and we have to change the way that we deal with it because we can't be in a situation in these areas of conflict where we are being pushed around by another nation," he told ITV's Good Morning Britain.

Economic sanctions on the Russian elite may have more bite, but would require greater political will.

Mr Skripal, 66, was convicted of passing secrets to MI6 but was given refuge in the UK in 2010 as part of a "spy swap".

It is known that he and his 33-year-old daughter had visited the Mill pub and Zizzi restaurant in Salisbury on Sunday afternoon, before they were found collapsed on a bench near the Maltings shopping centre.

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